HONG KONG, Oct 19 (Reuters) - A decision on the future of Hong Kong-listed Hanergy Thin Film Power Group could come within weeks after the solar panel equipment maker met regulators last month as part of efforts to end a three-year trading suspension, sources said.

Hanergy’s stock collapsed spectacularly in May 2015, when, after a five-fold increase over the previous 12 months, it plunged 47 percent in 24 minutes, wiping out $19 billion in market capitalisation before the company asked for the shares to be suspended.

The case is being watched for what it reveals of the regulator’s toughened stance towards listed companies after it became more proactive in probing suspicious share price moves in response to several high-profile stock crashes.

In a sign that a decision on a resumption of trading could be pending, Hanergy executives met with the Securities and Futures Commission (SFC) in late September as part of the regulator’s investigation, sources with knowledge of the matter said.

A decision on a resumption is usually delivered by the regulator within a month of such a hearing, one of the sources said, although they warned a ruling in this case could take longer. The SFC’s decision cannot be appealed by the company.

Hanergy and the SFC declined to comment. The sources declined to be identified because the hearing was private and they were not authorised to speak to the media.

The SFC announced an investigation after Hanergy’s collapse and slapped its own trading suspension on the company - meaning it would need regulatory approval to resume trading.

Last year as part of that process former Hanergy chairman Li Hejun - founder and owner of its unlisted mainland parent, and majority owner of its Hong Kong-listed unit - was disqualified from holding a directorship in Hong Kong for eight years and from being involved in the management of any listed or unlisted group in the city.

Four non-executive directors of Hanergy received lesser disqualifications.

The regulator also asked for published details of the company’s activities, business, assets, liabilities and financial performance. That document was published in April.

September’s meeting in Hong Kong between Hanergy executives and the SFC lasted for about four hours and focused on the company’s future business plan, one of the sources said.

The company warned in August that it faced forced delisting under stock exchange rules if its shares did not resume trading by July 31 next year.

The decision about Hanergy comes as the city’s bourse, Hong Kong Exchanges and Clearing, is discussing the merits of introducing automatic suspensions for certain accounting transgressions to better protect investors.

Critics of suspensions argue it leaves small shareholders unable to sell for months or potentially years - including those of Hanergy.

There has been no official market for Hanergy stock since the shares were suspended at HK$3.91 on May 20 2015. However Li offloaded shares in December 2015 at 0.18 yuan each, according to a regulatory filing. ($1 = 6.9369 Chinese yuan renminbi) (Reporting by Clare Jim; Additional reporting by Alun John and Jennifer Hughes; Editing by Stephen Coates)